1. Field of the Invention
The present invention relates to a hand tool, and more particularly to a hand tool with an adjustable rotational speed and torsion force to change the rotational speed and the output torsion force of a tool holder of the hand tool.
2. Description of Related Art
A conventional pneumatic hand tool in accordance with the prior art shown in FIG. 8 comprises an L-shaped body (6) having a first section and a second section. A motor (62) is mounted in the first section of the body (6) and has an axle (621) partially received in the motor (62). A first bevel gear (623) is mounted on a free end of the axle (621). An output axle (7) is longitudinally and rotatably mounted in the second section of the body (6). A second bevel gear (624) is securely mounted around the output axle (7) and engaged the first bevel gear (621). A tool holder (8) is partially rotatably received in the body (6) and fixedly connected to one end of the output axle (7). The second bevel gear and the output axle (7) are driven by the first bevel gear (623) to drive tool holder (8) when the motor (62) is operated.
The conventional pneumatic hand tool is usually used to drive a screw or drill a hold. However, to drive a screw needs a torsion force greater than that to drill hole. The conventional pneumatic hand tool has no device to change the output rotational speed and torsion force such that the conventional is not suitable to various work types. Consequently, an adjusting valve (63) is mounted to the body (6) to control a compressed air current that flows into the body (6) to drive the motor. A small air current will cause a slow rotational speed and a small torsion force. However, a small torsion force is hard to filly drive a screw into a work piece.
With reference to FIG. 9 that shows a second conventional hand tool. The second conventional hand tool has a body (9) and an output axle (91) rotatably mounted in the body (9). The output axle (91) is driven by a motor (not shown) and has a free end. A first planet gear set (92) and a second planet gear set (93) are sequentially mounted on the free end of the output axle (91). Consequently, the second conventional hand tool can provide a torsion force greater than that of the above conventional hand tool. However, the output rotational speed and torsion force of the second conventional hand tool still cannot be changed to suit various work condition.
The present invention has arisen to mitigate and/or obviate the disadvantages of the two conventional hand tools.
The main objective of the present invention is to provide an improved hand tool with an adjustable rotational speed and torsion force.
To achieve the objective, the hand tool in accordance with the present invention comprises a shaft rotatably received in a body of the hand tool and driven by a motor that is mounted in the body. A first planet gear set is longitudinally connected to one end of the shaft opposite to the motor and a second planet gear set is longitudinally connected to the first planet gear set. The shaft is longitudinally movable in the body. The hand tool only has the first planet gear set acted thereon when the shaft is pushed toward the second planet gear set. The first planet gear set and the second planet gear set are acted on the hand tool at the same time when the shaft is pulled.